Define planets by size, not orbit
This is something I've thought about for a while but it doesn't seem to get a lot of support from fellow space geeks. I say scrap the entire "moon" concept and define anything with a diameter larger than 2000 km as a planet. Anything smaller than that down to 100 km a planetoid, and anything smaller than that either an asteroid or comet.
This would mean Luna, Ganymede, Io, Europa, Callisto, Titan, Triton, and Pluto all qualify as planets. Charon, Miranda, Titania, etc etc would become planetoids. Phobos would be a captured asteroid. Such a concept might meet with a lot of resistance but it would bring consistancy to classifying heavenly bodies.